The latest Firefox beta is rather awesome, with tabs on top, and a new menu that looks like an awful lot like Opera. It's very slick, until you try installing extensions that haven't updated yet. Here's how to force them to work.

Windows/Mac/Linux: Mozilla today released the first beta build of Firefox 4, complete with a new…
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Here's the error message we're talking about:

Side note: want to test the new beta out for yourself? Head over to the Firefox beta site.

Open up the about:config page, and then right-click anywhere and choose New –> Boolean.

You'll get a popup menu, at which point you'll want to use one of the two values as the preference name, depending on the version you're using:

4.0 Beta: extensions.checkCompatibility.4.0b

4.0 Release: extensions.checkCompatibility.4.0

Then set the value to false.

At this point your extensions should install just fine…

Important Note: At the moment of the writing of this article, Greasemonkey is really actually incompatible with Firefox 4.0 beta, and continually opens up the homepage with a never-ending list of tabs. The same goes for quite a few extensions that we tested, though some of them worked fine. We're pretty sure they'll be updated very soon.